17.1 Introduction
Cyclodextrins (CDs) as a class of cyclic oligosaccharides are formed by the linkage
of D-(+)-glucopyranoses via 1,4-α-glucosidic bond. And they are industrially produced via amylose zymolysis under the existence of glucose transferase generated by
bacillus [1]. The most common CDs are α-, β-, and γ-CDs, which contain 6, 7, and
8 glucopyranose units, respectively. Stable intramolecular hydrogen bonding allows
these cavities with different sizes (internal diameters are 5 Å, 6.5 Å, and 8.5 Å in
turn) have the same depth of 7.9 Å. Among them, the hydrophilic hydroxyl groups
formed the primary surfaces (6-OH) and the secondary surfaces (2-OH, 3-OH) of the
CD units, while the ether bond and the carbon-hydrogen bond constitute their
hydrophobic cavities [2, 3]. Therefore, CDs as a macrocyclic host with good water
solubility and biocompatibility, with specific recognition and bonding abilities with
inorganic, organic, and biological substrates and polymer chains [4–8], are gaining
an increasing number of chemists’ attention.
Gels, combining the elasticity of solid and the fluidity of liquid, occupy an
extremely important position in the field of soft materials. Lots of supramolecular
gels based on CDs have been constructed through a variety of non-covalent interactions, such as hydrogen binding between polymer chain-threaded CDs [9]; hostguest interactions between CDs with adamantane [10], azobenzene [11, 12],
glycyrrhetinic acid [13], ferrocene [14], and naphthalene [15, 16] and their derivatives; and ionic interaction between anion- or cation-modified CD derivatives and
polycations or polyanions [17]. Supramolecular gels based on CDs have been widely
applied in many fields. For example, (1) owning to CDs’ good solubility and
biocompatibility, CD hydrogels have been used to load anticancer drugs doxorubicin
(DOX) [18, 19], paclitaxel (PTX) [20], camptothecin (CPT) [21–23], cisplatin [24],
etc. to achieve sustained release and enhanced anticancer effect; (2) the polyhydroxyl structure of supramolecular CD gels offers possibilities for molecule
imprinting of saccharides [25, 26]; (3) the porous structure of CD gels also provides
a series of applications in the removal of environmental contaminants [27, 28] and
heavy metal ions [29]; and (4) due to the dynamic bonding behavior of the CD host
to specific guests, the CD hydrogels play a special role in photosensitive materials,
pressure-sensitive materials, temperature-sensitive materials, intelligent adhesive
materials, and other smart materials [30]. In this chapter, the latest progresses in
the construction of CD hydrogels and their applications in various fields will be
reviewed. And we hope it can provide inspiration for the constructions and functions
of new supramolecular hydrogel materials based on CDs.
17.2 Construction of CD Gels
Using the specific recognition and binding of CDs and various guest molecules,
chemists have developed a variety of CD gels based on a series of supramolecular
interactions (hydrogen bonding, host-guest bonding, ionic interactions, etc.). In the
484
Q. Zhao et al.
Cyclodextrins (CDs) as a class of cyclic oligosaccharides are formed by the linkage
of D-(+)-glucopyranoses via 1,4-α-glucosidic bond. And they are industrially produced via amylose zymolysis under the existence of glucose transferase generated by
bacillus [1]. The most common CDs are α-, β-, and γ-CDs, which contain 6, 7, and
8 glucopyranose units, respectively. Stable intramolecular hydrogen bonding allows
these cavities with different sizes (internal diameters are 5 Å, 6.5 Å, and 8.5 Å in
turn) have the same depth of 7.9 Å. Among them, the hydrophilic hydroxyl groups
formed the primary surfaces (6-OH) and the secondary surfaces (2-OH, 3-OH) of the
CD units, while the ether bond and the carbon-hydrogen bond constitute their
hydrophobic cavities [2, 3]. Therefore, CDs as a macrocyclic host with good water
solubility and biocompatibility, with specific recognition and bonding abilities with
inorganic, organic, and biological substrates and polymer chains [4–8], are gaining
an increasing number of chemists’ attention.
Gels, combining the elasticity of solid and the fluidity of liquid, occupy an
extremely important position in the field of soft materials. Lots of supramolecular
gels based on CDs have been constructed through a variety of non-covalent interactions, such as hydrogen binding between polymer chain-threaded CDs [9]; hostguest interactions between CDs with adamantane [10], azobenzene [11, 12],
glycyrrhetinic acid [13], ferrocene [14], and naphthalene [15, 16] and their derivatives; and ionic interaction between anion- or cation-modified CD derivatives and
polycations or polyanions [17]. Supramolecular gels based on CDs have been widely
applied in many fields. For example, (1) owning to CDs’ good solubility and
biocompatibility, CD hydrogels have been used to load anticancer drugs doxorubicin
(DOX) [18, 19], paclitaxel (PTX) [20], camptothecin (CPT) [21–23], cisplatin [24],
etc. to achieve sustained release and enhanced anticancer effect; (2) the polyhydroxyl structure of supramolecular CD gels offers possibilities for molecule
imprinting of saccharides [25, 26]; (3) the porous structure of CD gels also provides
a series of applications in the removal of environmental contaminants [27, 28] and
heavy metal ions [29]; and (4) due to the dynamic bonding behavior of the CD host
to specific guests, the CD hydrogels play a special role in photosensitive materials,
pressure-sensitive materials, temperature-sensitive materials, intelligent adhesive
materials, and other smart materials [30]. In this chapter, the latest progresses in
the construction of CD hydrogels and their applications in various fields will be
reviewed. And we hope it can provide inspiration for the constructions and functions
of new supramolecular hydrogel materials based on CDs.
17.2 Construction of CD Gels
Using the specific recognition and binding of CDs and various guest molecules,
chemists have developed a variety of CD gels based on a series of supramolecular
interactions (hydrogen bonding, host-guest bonding, ionic interactions, etc.). In the
484
Q. Zhao et al.